fix: fix use utf_slice to use utf8_slice

src/collections/string.md

@@ -110,7 +110,7 @@ You can use [utf8_slice](https://docs.rs/utf8_slice/1.0.0/utf8_slice/fn.slice.ht
 
 **Example**
 ```rust
-use utf_slice;
+use utf8_slice;
 fn main() {
    let s = "The 🚀 goes to the 🌑!";
 

src/compound-types/string.md

@@ -254,7 +254,7 @@ You can use [utf8_slice](https://docs.rs/utf8_slice/1.0.0/utf8_slice/fn.slice.ht
 
 **Example**
 ```rust
-use utf_slice;
+use utf8_slice;
 fn main() {
    let s = "The 🚀 goes to the 🌑!";
 

zh-CN/src/collections/String.md

@@ -113,7 +113,7 @@ fn main() {
 
 **示例**
 ```rust
-use utf_slice;
+use utf8_slice;
 fn main() {
    let s = "The 🚀 goes to the 🌑!";
 

zh-CN/src/compound-types/string.md

@@ -245,7 +245,7 @@ fn main() {
 
 **Example**
 ```rust
-use utf_slice;
+use utf8_slice;
 fn main() {
    let s = "The 🚀 goes to the 🌑!";